Covalent polar lipid conjugates with neurologically active compounds for targeting

ABSTRACT

This invention herein describes a method of facilitating the entry of drugs into cells and tissues at physiologically protected sites at pharmicokinetically useful levels and also a method of targeting drugs to specific organelles within the cell. This polar lipid/drug conjugate targeting invention embodies an advance over other drug targeting methods known in the prior art, because the invention provides drug concentrations in such physiologically protected sites that can reach therapeutically-effective levels after administration of systemic levels much lower than are currently administered to achieve a therapeutic dose. This technology is appropriate for use with psychotropic, neurotropic and neurological drugs, agents and compounds, for rapid and efficient introduction of such agents across the blood-brain barrier. Further, the invention provides means for retention and prolonged enzymatic release of psychotropic, neurotropic and neurological drugs, agents and compounds comprising the conjugates of the invention, in the brain and central nervous system.

This application is a divisional of U.S. patent application Ser. No.08/923,015, filed Sep. 3, 1997, now U.S. Pat. No. 6,024,977, issued Feb.15, 2000, which is a divisional of U.S. patent application Ser. No.08/735,977, filed Oct. 25, 1996, now U.S. Pat. No. 5,827,819, issuedOct. 27, 1998, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/685,152, filed Jul. 23, 1996, now U.S. Pat. No.5,965,519, issued Oct. 12, 1999, which is a continuation-in-part of U.S.patent application Ser. No. 08/142,771, filed Oct. 26, 1993, now U.S.Pat. No. 5,543,389, issued Aug. 6, 1996, which is a continuation-in-partof U.S. patent application Ser. No. 07/911,209, filed Jul. 9, 1992, nowU.S. Pat. No. 5,256,641, issued Oct. 26, 1993, which is acontinuation-in-part of U.S. patent application Ser. No. 07/607,982,filed Nov. 1, 1990, now U.S. Pat. No. 5,149,794, issued Sep. 22, 1992,each of which are herein incorporated by reference.

This application is also related to U.S. patent application Ser. No.08/691,891, filed Aug. 1, 1996, now U.S. Pat. No. 5,840,674, issued Nov.24,1998, which is a continuation of U.S. patent application Ser. No.08/441,770, filed May 16, 1995, now U.S. Pat. No. 5,543,391, issued Aug.6, 1996, and U.S. patent application Ser. No. 08/246,941, filed May 19,1994, now U.S. Pat. No. 5,543,390, issued Aug. 6, 1996.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION

A major goal in the pharmacological arts has been the development ofmethods and compositions to facilitate the specific delivery oftherapeutic and other agents to the appropriate cells and tissues thatwould benefit from such treatment, and the avoidance of the generalphysiological effects of the inappropriate delivery of such agents toother cells or tissues of the body. One common example of the need forsuch specificity is in the field of neurologic agent therapy for thetreatment of diseases of the central nervous system, particularly thebrain, which is protected by a layer of endothelial cells and otherstructures collectively known as the blood-brain barrier. In thepharmacological and neurologic arts, it is well-recognized that theinability to deliver effective amounts of neurotropic, psychotropic andanticonvulsant drugs and agents across the blood-brain barrier severelylimits the therapeutic efficacy of such pharmaceutical compounds and canprevent treatment of neurologic disease. In addition, the use of eveneffective neurologic agents is further limited by systemic toxicityresulting from the high systemic concentrations that must beadministered to achieve a therapeutic concentration of such agents inthe brain, central nervous system and other neurological structures.Similar considerations apply in other organs and tissues in mammals thatare protected by such blood-related barriers, such as the testes.

In addition, it is recognized in the medical arts that certainsubcellular organelles are the sites of pharmacological action ofcertain drugs or are involved in the biological response to certainstimuli. Specific delivery of diagnostic or therapeutic compounds tosuch intracellular organelles is thus desirable to increase thespecificity and effectiveness of such clinical diagnostic or therapeutictechniques.

Drug Targeting

It is desirable to increase the efficiency and specificity ofadministration of a therapeutic agent to the cells of the relevanttissues protected by physiological barriers (i.e., such as theblood-brain barrier) in a variety of pathological states. This isparticularly important as relates to psychotropic, neurological andneurotropic agents. Such agents typically have systemic effects,including renal and hepatotoxicity, hematopoietic suppression,teratogenic capacity, partitioning into breast milk and otherpleiotropic cytotoxic effects that damage or otherwise deleteriouslyimpact on uninvolved cells and tissues. This is particularly the case indelivering psychotropic, neurotropic and neurological agents tophysiologically protected sites, since high systemic concentrations ofsuch agents are required to promote partitioning of a sufficient amountof the psychotropic, neurotropic and neurological agents into theprotected sites to achieve a therapeutic result. Thus, an efficientdelivery system which would enable the delivery of such drugsspecifically to cells and tissues in such physiologically protectedsites would increase the efficacy of treatment and reduce the associated“side effects” of such drug treatments, and also serve to reducemorbidity and mortality associated with clinical administration of suchdrugs.

Numerous methods for enhancing the biological activity and thespecificity of drug action have been proposed or attempted (see, forexample, Kreeger, 1996, The Scientist, Sep. 16, 1996, p. 6). To date,however, efficient or specific drug delivery remains to be predictablyachieved.

U.S. Pat. No. 5,017,566, issued May 21, 1991 to Bodor disclose β- andγ-cyclodextrin derivatives comprising inclusion complexes of lipoidalforms of dihydropyridine redox targeting moieties.

U.S. Pat. No. 5,023,252, issued Jun. 11, 1991 to Hseih disclose the useof pharmaceutical compositions comprising a neurologically active drugand a compound for facilitating transport of said drug across theblood-brain barrier including a macrocyclic ester, diester, amide,diamide, amidine, diamidine, thioester, dithioester, thioamide, ketoneor lactone.

U.S. Pat. No. 5,024,998, issued Jun. 18, 1991 to Bodor discloseparenteral solutions of aqueous-insoluble drugs with β- andγ-cyclodextrin derivatives.

U.S. Pat. No. 5,039,794, issued Aug. 13, 1991 to Wier et al. disclosethe use of a metastatic tumor-derived egress factor for facilitating thetransport of compounds across the blood-brain barrier.

U.S. Pat. No. 5,112,863, issued May 12, 1992 to Hashimoto et al.disclose the use of N-acyl amino acid derivatives as antipsychotic drugsfor delivery across the blood-brain barrier.

U.S. Pat. No. 5,124,146, issued Jun. 23, 1992 to Neuwelt disclose amethod for delivery of therapeutic agents across the blood-brain barrierat sites of increase permeability associated with brain lesions.

U.S. Pat. No. 5,153,179, issued Oct. 6, 1992 to Eibl disclose acylatedglycerol and derivatives for use in a medicament for improvedpenetration of cell membranes.

U.S. Pat. No. 5,177,064, issued Jan. 5, 1993 to Bodor disclose the useof lipoidal phosphonate derivatives of nucleoside antiviral agents fordelivery across the blood-brain barrier.

U.S. Pat. No. 5,254,342, issued Oct. 19, 1993 to Shen et al. disclosereceptor-mediated transcytosis of the blood-brain barrier using thetransferrin receptor in combination with pharmaceutical compounds thatenhance or accelerate this process.

U.S. Pat. No. 5,258,402, issued Nov. 2, 1993 to Maryanoff disclosetreatment of epilepsy with imidate derivatives of anticonvulsivesulfamate.

U.S. Pat. No. 5,270,312, issued Dec. 14, 1993 to Glase et al. disclosesubstituted piperazines as central nervous system agents.

U.S. Pat. No. 5,284,876, issued Feb. 8, 1994 to Shashoua et al.,disclose fatty acid conjugates of dopanergic drugs for tardivedyskinesia.

U.S. Pat. No. 5,389,623, issued Feb. 14, 1995 to Bodor disclose the useof lipoidal dihydropyridine derivatives of anti-inflammatory steroids orsteroid sex hormones for delivery across the blood-brain barrier.

U.S. Pat. No. 5,405,834, issued Apr. 11, 1995 to Bundgaard et al.disclose prodrug derivatives of thyrotropin releasing hormone.

U.S. Pat. No. 5,413,996, issued May 9, 1995 to Bodor discloseacyloxyalkyl phosphonate conjugates of neurologically-active drugs foranionic sequestration of such drugs in brain tissue.

U.S. Pat. No. 5,434,137, issued Jul. 18, 1995 to Black disclose methodsfor the selective opening of abnormal brain tissue capillaries usingbradykinin infused into the carotid artery.

U.S. Pat. No. 5,442,043, issued Aug. 15, 1995 to Fukuta et al. disclosea peptide conjugate between a peptide having a biological activity andincapable of crossing the blood-brain barrier and a peptide whichexhibits no biological activity and is capable of passing theblood-brain barrier by receptor-mediated endocytosis.

U.S. Pat. No. 5,466,683, issued Nov. 14, 1995 to Sterling et al.disclose water soluble analogues of the anticonvulsant Tegretol®(carbamazepine) for the treatment of epilepsy.

U.S. Pat. No.5,525,727, issued Jun. 11, 1996 to Bodor disclosecompositions for differential uptake and retention in brain tissuecomprising a conjugate of a narcotic analgesic and agonists andantagonists thereof with a lipoidal form of dihydropyridine that forms aredox salt upon uptake across the blood-brain barrier that preventspartitioning back to the systemic circulation thereafter.

International Patent Application Publication Number WO85/02342,published Jun. 6, 1985 for Max-Planck Institute disclose a drugcomposition comprising a glycerolipid or derivative thereof.

International Patent Application Publication Number WO89/11299,published Nov. 30, 1989 for State of Oregon disclose a chemicalconjugate of an antibody with a an enzyme which is deliveredspecifically to a brain lesion site for activating aseparately-administered neurologically-active prodrug.

International Patent Application Publication Number WO91/04014,published Apr. 4, 1991 for Synergen, Inc. disclose methods fordelivering therapeutic and diagnostic agents across the blood-brainbarrier by encapsulating said drugs in liposomes targeted to braintissue using transport-specific receptor ligands or antibodies.

International Patent Application Publication Number WO91/04745,published Apr. 18, 1991 for Athena Neurosciences, Inc. disclosetransport across the blood-brain barrier using cell adhesion moleculesand fragments thereof to increase the permeability of tight junctions invascular endothelium.

International Patent Application Publication Number WO91/14438,published Oct. 3, 1991 for Columbia University disclose the use of amodified, chimeric monoclonal antibody for facilitating transport ofsubstances across the blood-brain barrier.

International Patent Application Publication Number WO94/0113 1,published Jan. 20, 1994 for Eukarion, Inc. disclose lipidized proteins,including antibodies. International Patent Application PublicationNumber WO94/03424, published Feb. 17, 1994 for Ishikura et al. disclosethe use of amino acid derivatives as drug conjugates for facilitatingtransport across the blood-brain barrier.

International Patent Application Publication Number WO94/06450,published Mar. 31, 1994 for the University of Florida discloseconjugates of neurologically-active drugs with a dihydropyridine-typeredox targeting moiety and comprising an amino acid linkage and analiphatic residue.

International Patent Application Publication Number WO94/02178,published Feb. 3, 1994 for the U.S. Government, Department of Health andHuman Services disclose antibody-targeted liposomes for delivery acrossthe blood-brain barrier.

International Patent Application Publication Number WO95/07092,published Mar. 16, 1995 for the University of Medicine and Dentistry ofNew Jersey disclose the use of drug-growth factor conjugates fordelivering drugs across the blood-brain barrier.

International Patent Application Publication Number WO96/00537,published Jan. 11, 1996 for Southern Research Institute disclosepolymeric microspheres as injectable drug-delivery vehicles fordelivering bioactive agents to sites within the central nervous system.

International Patent Application Publication Number WO96/04001,published Feb. 15, 1996 for Molecular/Structural Biotechnologies, Inc.disclose omega-3-fatty acid conjugates of neurologically-active drugsfor brain tissue delivery.

International Patent Application Publication Number WO96/22303,published Jul. 25, 1996 for the Commonwealth Scientific and IndustrialResearch Organization disclose fatty acid and glycerolipid conjugates ofneurologically-active drugs for brain tissue delivery.

An additional challenge in designing an appropriate drug delivery schemeis to include within the drug conjugate a functionality which couldeither accelerate or reduce the rate at which the drug is released uponarrival at the desired site. Such a functionality would be especiallyvaluable if it allowed differential rates of drug release, or specificrelease only at the appropriate drug target site.

There remains a need in the art for an effective means for the specificdelivery of biologically-active compounds, particularly psychotropic,neurotropic and neurological drugs and agents, to physiologicallyrestricted or protected sites. Advantageous embodiments of such deliverymeans are formulated to efficiently deliver the biologically-activecompound to a physiologically-protected site, such as the brain orcentral nervous system, while minimizing hepatic and renal uptake of theagent or hematopoietic insult resulting therefrom.

SUMMARY OF THE INVENTION

The present invention is directed to an improved method for deliveringbiologically-active compounds, particularly drugs including preferablypsychotropic, neurotropic and neurologically-acting drugs, tophysiologically protected sites in an animal in vivo. This deliverysystem achieves specific delivery of such biologically-active compoundsthrough conjugating the compounds with a polar lipid carrier. Thisinvention has the specific advantage of facilitating the entry of suchcompounds into cells and tissues protected by such physiologicalbarriers as the blood-brain barrier via a polar lipid carrier, achievingeffective intracellular concentration of such compounds more efficientlyand with more specificity than conventional delivery systems.

The invention provides compositions of matter comprising abiologically-active compound covalently linked to a polar lipid carriermolecule. Preferred embodiments also comprise a spacer molecule havingtwo linker functional groups, wherein the spacer has a first end and asecond end and wherein the lipid is attached to the first end of thespacer through a first linker functional group and thebiologically-active compound is attached to the second end of the spacerthrough a second linker functional group. In preferred embodiments, thebiologically-active compound is a drug, most preferably a psychotropic,neurotropic or neurologically-acting drug or agent, or an antioxidant.Preferred polar lipids include but are not limited to acyl- and acylatedcarnitine, sphingosine, ceramide, phosphatidyl choline, phosphatidylglycerol, phosphatidyl ethanolamine, phosphatidyl inositol, phosphatidylserine, cardiolipin and phosphatidic acid. Preferred biologically-activecompounds include neurotropic agents such as L-dopa, hydroxytryptamineand metabolites thereof; amantadine, benztropine, bromocryptine,diphenhydramine, levadopa (a particularly preferred embodiment) andcombinations thereof (e.g., with carbidopa as provided as Sinemet®);pergolid, trihexphenidyl, ethosuximide, valproic acid, carbamazepine(e.g., Tegretol®) and, in a particularly preferred embodiment, the 10-or 11-hydroxy analogues of carbamazepine; primidone, gabapentin in aparticularly preferred embodiment; lamotrigine in a particularlypreferred embodiment; felbamate, paramethadione and trimethadione;phenothiazines, thioxanthemes and related compounds; clozapine,haldoperidol, loxapine (Loxitane®), benzodiazapene antidepressants ofthe norepinephrine reuptake inhibitor type; monoamine oxidaseinhibitors, and antioxidants such as carotenes, glutathione andN-acetylcysteine. Pharmaceutical compositions comprising the drug/polarlipid conjugates of the invention are also provided.

The invention also provides compositions of matter comprising abiologically-active compound covalently linked to a lipid, mostpreferably a polar lipid, carrier molecule via a spacer molecule whereinthe spacer allows the biologically-active compound to act without beingreleased at an intracellular site. In these embodiments of theinvention, the first linker functional group attached to the first endof the spacer is characterized as “strong” and the second linkerfunctional group attached to the second end of the spacer ischaracterized as “weak”, with reference to the propensity of thecovalent bonds between each end of the spacer molecule to be broken. Inother embodiments of the compositions of matter of the invention, thespacer allows the facilitated hydrolytic release of thebiologically-active compound at an intracellular site. Other embodimentsof the spacer facilitate the enzymatic release of thebiologically-active compound at an intracellular site. In particularlypreferred embodiments, the spacer functional group is hydrolyzed by anenzymatic activity found in brain tissue, including neuronal, glial andother brain cell types, preferably an esterase and most preferably anesterase having a differential expression and activity profile in theappropriate target cell type. In additional preferred embodiments,specific release of biologically-active compounds is achieved byenzymatic or chemical release of the biologically-active compound byextracellular cleavage of a cleavable linker moiety via an enzymaticactivity specific for brain tissue, with resulting specific uptake ofthe released psychotropic, neurotropic or neurological agent by theappropriate cell in said tissue.

In another embodiment of this aspect of the invention, the spacermolecule is a peptide of formula (amino acid)_(n), wherein n is aninteger between 2 and 25, preferably wherein the peptide comprises apolymer of one or more amino acids. In other embodiments of thecompositions of matter of the invention, the biologically-activecompound of the invention has a first functional linker group, and alipid, most preferably a polar lipid, carrier has a second functionallinker group, and the compound is covalently linked directly to thelipid carrier by a chemical bond between the first and second functionallinker groups. In preferred embodiments, each of the first and secondfunctional linker groups is a hydroxyl group, a primary or secondaryamino group, a phosphate group or substituted derivatives thereof or acarboxylic acid group. In another aspect of the invention is providedcompositions of matter comprising a drug, most preferably an apsychotropic, neurotropic or neurological drug or agent, covalentlylinked to a polar lipid carrier molecule. Preferred embodiments alsocomprise a spacer molecule having two linker functional groups, whereinthe spacer has a first end and a second end and wherein the lipid isattached to the first end of the spacer through a first linkerfunctional group and the drug is attached to the second end of thespacer through a second linker functional group. Preferred embodimentsof the invention are provided wherein the drug is a psychotropic,neurotropic or neurological drug or agent. Preferred polar lipidsinclude but are not limited to acyl- and acylated carnitine,sphingosine, ceramide, phosphatidyl choline, phosphatidyl glycerol,phosphatidyl ethanolamine, phosphatidyl inositol, phosphatidyl serine,cardiolipin and phosphatidic acid. Preferred psychotropic, neurotropicor neurological drugs or agents comprising the conjugates of theinvention include L-dopa, hydroxytryptamine and metabolites thereof;amantadine, benztropine, bromocryptine, diphenhydramine, levadopa (aparticularly preferred embodiment) and combinations thereof (e.g., withcarbidopa as provided as Sinemet®); pergolid, trihexphenidyl,ethosuximide, valproic acid, carbamazepine (e.g., Tegretol®) and, in aparticularly preferred embodiment, the 10- or 11-hydroxy analogues ofcarbamazepine; primidone, gabapentin in a particularly preferredembodiment; lamotrigine in a particularly preferred embodiment;felbamate, paramethadione and trimethadione; phenothiazines,thioxanthemes and related compounds; clozapine, haldoperidol, loxapine(Loxitane®), benzodiazapene antidepressants of the norepinephrinereuptake inhibitor type; monoamine oxidase inhibitors, and antioxidantssuch as carotenes, glutathione and N-acetylcysteine. Pharmaceuticalcompositions comprising the drug/polar lipid conjugates of the inventionare also provided.

The invention also provides compositions of matter comprising apsychotropic, neurotropic or neurological drug or agent, covalentlylinked to a polar lipid carrier molecule via a spacer molecule, whereinthe spacer allows the drug to act without being released at anintracellular site. In these embodiments of the invention, the firstlinker functional group attached to the first end of the spacer ischaracterized as “strong” and the second linker functional groupattached to the second end of the spacer is characterized as “weak”,with reference to the propensity of the covalent bonds between each endof the spacer molecule to be broken.

In other embodiments of the compositions of matter of the invention, thespacer allows the facilitated hydrolytic release of a psychotropic,neurotropic or neurological drug or agent at an intracellular site.Other embodiments of the spacer facilitate the enzymatic release of thepsychotropic, neurotropic or neurological drug or agent of the inventionat an intracellular site. In particularly preferred embodiments, thespacer functional group is hydrolyzed by an enzymatic activity found ina physiologically-protected site, such as the brain and central nervoussystem and more particularly including neuronal, glial and other braincell types, wherein said enzymatic activity is preferably an esteraseand most preferably an esterase having a differential expression andactivity profile in different tissue cell types. In additional preferredembodiments, specific release of the psychotropic, neurotropic orneurological drug or agent of the invention is achieved by enzymatic orchemical release of these drugs by extracellular cleavage of a cleavablelinker moiety via an enzymatic activity specific for,for example, braintissue, followed by specific uptake of the released psychotropic,neurotropic or neurological drug or agent by the appropriate cell insaid tissue.

In another embodiment of this aspect of the invention, the spacermolecule is a peptide of formula (amino acid)_(n), wherein n is aninteger between 2 and 25, preferably wherein the peptide comprises apolymer of one or more amino acids.

In still further embodiments of the compositions of matter of theinvention are provided psychotropic, neurotropic or neurological drugsor agents having a first functional linker group, and a polar lipidcarrier having a second functional linker group, wherein the drug iscovalently linked directly to the polar lipid carrier by a chemical bondbetween the first and second functional linker groups. In preferredembodiments, each of the first and second functional linker groups is ahydroxyl group, a primary or secondary amino group, a phosphate group orsubstituted derivatives thereof or a carboxylic acid group. Preferredpsychotropic, neurotropic or neurological drugs or agents comprising theconjugates of the invention include L-dopa, hydroxytryptamine andmetabolites thereof; amantadine, benztropine, bromocryptine,diphenhydramine, levadopa (a particularly preferred embodiment) andcombinations thereof (e.g., with carbidopa as provided as Sinemet®);pergolid, trihexphenidyl, ethosuximide, valproic acid, carbamazepine(e.g., Tegretol®) and, in a particularly preferred embodiment, the 10-or 11-hydroxy analogues of carbamazepine; primidone, gabapentin in aparticularly preferred embodiment; lamotrigine in a particularlypreferred embodiment; felbamate, paramethadione and trimethadione;phenothiazines, thioxanthemes and related compounds; clozapine,haldoperidol, loxapine (Loxitane®), benzodiazapene antidepressants ofthe norepinephrine reuptake inhibitor type; monoamine oxidaseinhibitors, and antioxidants such as carotenes, glutathione andN-acetylcysteine. Preferred polar lipids include but are not limited toacyl- and acylated camitine, sphingosine, ceramide, phosphatidylcholine, phosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidylinositol, phosphatidyl serine, cardiolipin and phosphatidic acid.Pharmaceutical compositions comprising the drug/polar lipid conjugatesof the invention are also provided.

Preferred embodiments of this aspect of the invention includecompositions of matter that are polar lipid conjugates of anticonvulsiveagents, antiparkinsonian drugs, alkaloids, catecholamines includingdopamine analogues and derivatives, muscarinic receptor agonists andantagonists, cholinergic receptor agonists and antagonists, calciumchannel blockers, γ-aminobutyric acid (GABA) receptor agonists,antagonists, and uptake inhibitors and enhancers; phenothiazines,thioxanthemes and related compounds; clozapine, haldoperidol, loxapine(Loxitane®), benzodiazapene antidepressants of the norepinephrinereuptake inhibitor type; monoamine oxidase inhibitors; antidepressantsand antimanic agents, antioxidants and other compounds that mitigate theeffects of reactive oxygen species (for the treatment of Alzheimer'sdisease, Parkinson's disease, or other neurodegenerative conditions suchas ataxia telangiectasia and amyelolaterosclerosis (ALS)).

As disclosed herein, the invention comprehends a polar lipid-drugconjugate wherein the polar lipid selectively promotes association withand transit across certain physiological barriers to protected tissuesites, thereby facilitating delivery of drugs and other pharmaceuticalagents to such physiologically restricted or protected sites. Inembodiments comprising a spacer moiety, the spacer component of theconjugates of the invention will preferably act to specifically releasethe drug from the lipid at the target site; prevent the non-specificrelease from the drug from the lipid in the systemic circulation or inhepatic, renal or other inappropriate cells, tissue or organs; targetthe conjugate to a specific cell or cell type within the protectedtissue; prevent interaction and/or uptake of the drug by hematopoietic,ocular, hepatic or renal tissues; or perform other functions to maximizethe effectiveness of the drug.

This type of conjugate has numerous advantages. The drug-lipidconjugates of the invention provide delivery of a variety ofpsychotropic, neurotropic and neurological drugs and agents tophysiologically restricted or protected sites in vivo at concentrationsand pharmicokinetic rates not heretofore attainable. A benefit of thisadvantage is the achievement of therapeutic indices of agents in suchprotected sites whereby the agent is useful for achieving a desiredtherapeutic goal. Another benefit is decreased hepatic toxicity,hematopoietic suppression (such as thrombocytopenia, leukopenia, aplastic anemia, leukocytosis, eosinophilia, pancytopenia,agranulocytosis), reduced systemic metabolism, degradation and toxicity,reduced hepatic clearance, reduced systemic adverse drug interactions,and generally reduced side effects due to the achievement of a lower,therapeutically-effective dose as the result of surmounting thephysiological barrier. These biological effects can also result insimplified dosage schedules, particularly for drugs with short systemichalf-lives.

In addition, the lipid/drug conjugates promote the intracellular entryof a variety of potentially useful drugs at pharmokinetic rates notcurrently attainable. The range of targeted cell types is not limitedper se by particular, limited biological properties of the cell (such asthe number and type of specific receptor molecules expressed on the cellsurface). In contrast to traditional attempts to simply target drugs tospecific cells, the conjugates of the invention can also target drugs tospecific intracellular organelles and other intracellular compartments.In certain preferred embodiment, the conjugates of the inventionincorporate a variable spacer region that may allowpharmacologically-relevant rates of drug release from polar lipidcarrier molecules to be engineered into the compositions of theinvention, thereby increasing their clinical efficacy and usefulness.Thus, time-dependent drug release and specific drug release in cellsexpressing the appropriate degradative enzymes are a unique possibilityusing the drug-lipid conjugates of the invention.

In particular, felicitous design of the psychotropic,neurotropic/neurological drug/spacer/polar lipid conjugate can providean in vivo reservoir of time-dependent drug release in thephysiologically protected tissue, resulting in specific delivery oftherapeutic amounts to such tissues using a reduced dosage regime tominimize nonspecific, systemic and deleterious side effects. In suchformulations, the amount and activity of the psychotropic, neurotropicor neurological drug can be modulated by release via cleavage,preferably hydrolytic cleavage, of the spacer moiety, most preferably byan enzymatic activity in the protected tissue (e.g., brain) that has adifferential pattern of expression or activity in different cell typesin said tissue. The conjugates of the invention can also be combinedwith other drug delivery approaches to further increase specificity andto take advantage of useful advances in the art.

Specific preferred embodiments of the present invention will becomeevident from the following more detailed description of certainpreferred embodiments and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B depict the synthetic scheme put forth in Example 1.

FIG. 2A and FIG. 2B depict the synthetic scheme put forth in Example 2.

FIG. 3A and FIG. 3B depict the synthetic scheme put forth in Example 3.

FIG. 4 depicts the synthetic scheme put forth in Example 4.

FIG. 5 depicts the synthetic scheme put forth in Example 5.

FIGS. 6A through 6D depict prodrugs tested as in Example 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides compositions of matter and methods forfacilitating the entry into cells of biologically-active compounds. Forthe purposes of this invention, the term “biologically-active compound”is intended to encompass all naturally-occurring or synthetic compoundscapable of eliciting a biological response or having an effect, eitherbeneficial or cytotoxic, on biological systems, particularly cells andcellular organelles. These compounds are intended to include but are notlimited to all varieties of drugs, particularly psychotropic,neurotropic and neurologically-acting drugs and agents.

As used herein the terms “psychotropic, neurotropic andneurologically-acting drugs and agents” are intended to include anydrug, agent or compound having a neurological, neurotropic, orpsychotropic effect in an animal, preferably a human. These terms areintended to encompass anti-inflammatory agents, corticosteroids,sedatives, tranquilizers, narcotics, analgesics, anesthetics,anticonvulsive and antispasmodic agents, antiparkinsonian drugs,alkaloids, catecholamines, including dopamine analogues and derivatives,muscarinic receptor agonists and antagonists, cholinergic receptoragonists and antagonists, calcium channel blockers, γ-aminobutyric acid(GABA) receptor agonists, antagonists, and uptake inhibitors andenhancers; phenothiazines, thioxanthemes and related compounds;clozapine, haldoperidol, loxapine (Loxitane®), benzodiazapeneantidepressants of the norepinephrine reuptake inhibitor type; monoamineoxidase inhibitors; antidepressants and antimanic agents, antioxidantssuch as carotenes, glutathione, N-acetylcysteine or other molecules thatmitigate the effects of reactive oxygen species for the treatment ofAlzheimer's disease, Parkinson's disease, or other neurodegenerativeconditions such as ataxia telangiectasia and amyelolaterosclerosis(ALS); neuroregenerative agents; and agents for the treatment ofischemia and other vascular diseases of the central nervous system.Appropriate formulations and pharmaceutical compositions of theneurotropic/neurological/psychotropic drug/ polar lipid conjugates ofthe invention will be apparent and within the skill of one of ordinaryskill in this art to advantageously prepare in view of the instantdisclosure.

The compositions of matter provided by the invention comprise thebiologically-active compounds of the invention covalently linked to apolar lipid carrier. A polar lipid carrier, as defined herein isintended to mean any polar lipid having an affinity for, or capable ofcrossing, a biological membrane and in particular a physiologicalbarrier protecting certain cells, tissues and organs, including but notlimited to sphingosine, ceramide, phosphatidyl choline, phosphatidylglycerol, phosphatidyl ethanolamine, phosphatidyl inositol, phosphatidylserine, cardiolipin, phosphatidic acid, sphingomyelin and othersphingolipids, as these terms are understood in the art (see, Lehninger,Biochemistry, 2d ed., Chapters 11 & 24, Worth Publishers: New York,1975). Additionally, certain other lipids, such as acylated carnitine,comprise the conjugates of the invention (see Small, 1986, “From alkanesto phospholipids,” Handbook of Lipid Research: Physical Chemistry ofLipids, Volume 4, Chapters 4 and 12, Plenum Press: New York). For thepurposes of this invention, the term “polar lipid” is not intended toencompass “lipoid”-type compounds, such as, for example, aliphaticphosphonates (see, for example, U.S. Pat. No. 5,413,996).

The compositions of matter of the invention may be further comprised ofa spacer moiety comprising a first end and a second end, each end of thespacer having a functional linking group. For the purposes of thisinvention, the term “spacer” or “spacer moiety” is intended to encompassany chemical entity that links the biologically-active compound and thepolar lipid. Such spacer moieties may be designed to facilitate theattachment of the conjugates of the invention to a target cell, or tofacilitate, influence, modulate or regulate the release of thebiologically-active compound at the desired target site. Such spacersmay also facilitate enzymatic release at certain intracellular sites.Spacer groups, as described herein, include, but are not limited toaminohexanoic acid, polyglycine, polyamides, polyethylenes, and shortfunctionalized polymers having a carbon backbone which is from one toabout twelve carbon molecules in length. Particularly preferredembodiments of such spacer moieties comprise peptides of formula (aminoacid)_(n), wherein n is an integer between 2 and 25 and the peptide is apolymer of one or more amino acids.

The term “linker functional group” is defined herein as any functionalgroup for covalently binding the polar lipid carrier orbiologically-active agent to the spacer group. These groups can bedesignated either “weak” or “strong” based on the stability of thecovalent bond which the linker functional group will form between thespacer and either the polar lipid carrier or the biologically-activecompound. The weak functionalities include, but are not limited tophosphoramide, phosphoester, carbonate, amide, carboxyl-phosphorylanhydride, thioester and most preferably ester. The strongfunctionalities include, but are not limited to ether, thioether, amine,amide and most preferably ester. The use of a strong linker functionalgroup between the spacer group and the biologically-active compound willtend to decrease the rate at which the compound will be released at thetarget site, whereas the use of a weak linker functional group betweenthe spacer group and the compound may act to facilitate release of thecompound at the target site. Enzymatic release is, of course, alsopossible, but such enzyme-mediated modes of release will not necessarilybe correlated with bond strength in such embodiments of the invention.Spacer moieties comprising enzyme active site recognition groups, suchas spacer groups comprising peptides having proteolytic cleavage sitestherein, are envisioned as being within the scope of the presentinvention. Specifically, such specifically-cleavable peptides arepreferably prepared so as to be recognized by enzymes present in brainand other physiologically restricted or protected sites in vivo, so thatthe drug is preferentially liberated from the polar lipid conjugate atappropriate drug delivery sites. An illustrative example of such aspecifically-cleavable peptide is a portion of the proopiomelanocortinfamily of peptides, which are cleaved in mammalian brain tissue torelease a variety of peptides hormones and effector molecules, such asthe enkephalins. Other beneficial and advantageousspecifically-cleavable peptides will be recognized by those of ordinaryskill in the art.

The drug/polar lipid conjugates of the invention are preferably providedcomprised of spacer moieties that impart differential release propertieson the conjugates related to differential expression or activity ofenzymatic activities in physiologically restricted or protected sites incomparison with such activities in systemic circulation or ininappropriate targets, such as hepatic, renal or hematopoietic tissues.Differential release is also provided in certain embodiments in specificcell types comprising such physiologically protected tissues.

In particularly preferred embodiments of the present invention areprovided psychotropic/neurotropic/neurological drug/polar lipidconjugates for specific delivery to brain tissue for the alleviation oramelioration of pathological disease states in the brain. Thus, thepresent invention provides methods and compositions of matter forfacilitating the transit of such polar lipid conjugates of psychotropic,neurotropic or neurological drugs, agents and compounds across theblood-brain barrier and into targeted regions of the brain, for thetreatment of animal, preferably human, diseases and pathologicalconditions. Among the most common such diseases and conditions areAlzheimer's disease, Parkinson's disease, epilepsy and other seizuredisorders (such as petit mal, grand mal, tonic-clonic seizure disorder,parietal complex seizure, and psychomotor seizures), migraine,neurodegenerative conditions such as ataxia telangiectasia and ALS,Lennox-Gastaut syndrome, neuropathy such as trigeminal neuralgia,diabetic neuropathy, shingles, and psychological disorders, includingbipolar disorder, explosive aggression, depression and agitationassociated with elderly dementia.

The invention provides polar lipid/drug conjugates comprisingpsychotropic, neurotropic and neurological drugs, agents and compoundsincluding but not limited to L-dopa, hydroxytryptamine and metabolitesthereof; amantadine, benztropine, bromocryptine, diphenhydramine,levadopa (a particularly preferred embodiment) and combinations thereof(e.g., with carbidopa as provided as Sinemet®); pergolid,trihexphenidyl, ethosuximide, valproic acid, carbamazepine (e.g.,Tegretol®) and, in a particularly preferred embodiment, the 10- or11-hydroxy analogues of carbamazepine; primidone, gabapentin in aparticularly preferred embodiment; lamotrigine in a particularlypreferred embodiment; felbamate, paramethadione and trimethadione;phenothiazines, thioxanthemes and related compounds; clozapine,haldoperidol, loxapine (Loxitane®), benzodiazapene antidepressants ofthe norepinephrine reuptake inhibitor type; monoamine oxidaseinhibitors, and antioxidants such as carotenes, glutathione andN-acetylcysteine.

The invention specifically provides methods for preparing andadministering such psychotropic, neurotropic and neurological drugs,agent and compounds for use in treating pathological conditions in vivo.

Animals to be treated with the drug-polar lipid conjugates using themethods of the invention are intended to include all vertebrate animals,preferably domesticated animals, such as cattle, horses, goats, sheep,fowl, fish, household pets, and others, as well as wild animals, andmost preferably humans.

The following Examples illustrate certain aspects of the above-describedmethod and advantageous results. The following examples are shown by wayof illustration and not by way of limitation.

EXAMPLE 1

A polar lipid conjugate with levadopa is prepared by conjugating alinker moiety to a polar lipid via an amide linkage, as follows. A polarlipid (sphingosine) comprising unconjugated amino groups is reacted witha 6-hydroxyhexanoic acid (6-HHA) in the presence of 1.0 equivalent ofdicyclohexyl carbodiimide (DCCD) overnight at 40-50° C. The derivatizedsphingosine was then reacted with 0.1N methanolic potassium hydroxide atroom temperature, and then treated with 2.0 equivalents of tert-butyldimethyl silyl imidazole (TBDMS) overnight at 40-50° C. This sphingosinespecies, derivatized by an amide linkage between the amino group ofsphingosine and the carboxylate group of 6-HHA, is then esterified atthe unprotected 6-HHA derived hydroxyl group with bis-TBDMS-levadopa andDCCD overnight at 40-50° C. The levadopa-sphingosine conjugate is thendeprotected by treatment with 4.-0 equivalents of t-butylammoniumfluoride at 0° C. for 10 minutes. This reaction scheme is illustrated inFIG. 1. Synthesis of conjugates comprising ester linkages as describedin Examples 1, 2 and 3, and of amine linkages as described in Examples 4and 5 advantageously permits control of rates of drug release based ondifferences in amount and rates of amidase or esterase enzymaticactivity in the brain, wherein amidase-sensitive linkages generallyprovide a longer time release course than esterase-sensitive linkages.

EXAMPLE 2

A polar lipid conjugate with gabapentin comprising an ester linkage isprepared by conjugating a linker moiety to a polar lipid via an amidelinkage, as follows. A polar lipid (sphingosine) comprising unconjugatedamino groups is reacted with a 6-hydroxyhexanoic acid (6-HHA) in thepresence of 1.0 equivalent of dicyclohexyl carbodiimide (DCCD) overnightat 40-50° C. The derivatized sphingosine was then reacted with 0.1Nmethanolic potassium hydroxide at room temperature, and then treatedwith 2.0 equivalents of tert-butyl dimethyl silyl imidazole (TBDMS)overnight at 40-50° C. This sphingosine species, derivatized by an amidelinkage between the amino group of sphingosine and the carboxylate groupof 6-HHA, is then esterified at the unprotected 6-HHA derived hydroxylgroup with gabapentin and DCCD overnight at 40-50° C. Thegabapentin-sphingosine conjugate is then deprotected by treatment with4.-0equivalents oft-butylammonium fluoride at 0° C. for 10 minutes. Thisreaction scheme is illustrated in FIG. 2.

EXAMPLE 3

A polar lipid conjugate with 10-hydroxycarbamazepine comprising an esterlinkage is prepared by conjugating a linker moiety to a polar lipid viaan amide linkage, as follows. A polar lipid (sphingosine) comprisingunconjugated amino groups is reacted with a 6-hydroxyhexanoic acid(6-HHA) in the presence of 1.0 equivalent of dicyclohexyl carbodiimide(DCCD) overnight at 40-50° C. The derivatized sphingosine was thenreacted with 0.1N methanolic potassium hydroxide at room temperature,and then treated with 2.0 equivalents of tert-butyl dimethyl silylimidazole (TBDMS) overnight at 40-50° C. This sphingosine species,derivatized by an amide linkage between the amino group of sphingosineand the carboxylate group of 6-HHA, is then esterified at theunprotected 6-HHA derived hydroxyl group with 10-hydroxycarbamazepineand DCCD overnight at 40-50° C. The 10-hydroxycarbamazepine-sphingosineconjugate is then deprotected by treatment with 4.-0equivalents oft-butylammonium fluoride at 0° C. for 10 minutes. This reaction schemeis illustrated in FIG. 3.

EXAMPLE 4

A polar lipid conjugate of gabapentin, hydroxycarbamazepine or levadopais prepared by conjugating a specifically-cleavable peptide as a linkerbetween a polar lipid and a drug as follows. An derivatized polar lipidcomprising unconjugated amino groups is reacted with aproteolytically-inert peptide in which the terminal amine and any of theconstituent amino acid sidechain reactive amines are covered bytert-butoxycarbonyl (t-Boc) protecting groups in the presence oftriphenyl phosphine as described by Kishimoto (1975, Chem. Phys. Lipids15: 33-36). The peptide/polar lipid conjugate is then reacted in thepresence of pyridine hydrofluoride as described by Matsuura et al.(1976, J. Chem. Soc. Chem. Comm. xx: 451-459) to remove the t-Bocprotecting groups. The peptide/polar lipid is then conjugated to thespecifically-cleavable peptide, in which the terminal amine and any ofthe constituent amino acid sidechain reactive amines are covered byt-Boc protecting groups, as described in the presence of triphenylphosphine. After deprotection of reactive amines with pyridinehydrofluoride as described, gabapentin, hydroxycarbamazepine or levadopais conjugated to a free amino group of the polarlipid/peptide/specifically-cleavable peptide via a reactive carboxylicacid group to yield a drug/polar lipid conjugate of the invention. Thisreaction scheme is illustrated in FIG. 4 for sphingosine conjugated tolevadopa.

EXAMPLE 5

Carbamazepine is directly conjugated to sphingosine via an amide linkageas follows. Sphingosine is reacted with 1,3 bis(trimethylsilyl)urea asdescribed by Verbloom et al. (1981, Synthesis 1032: 807-809) to give atrimethylsilyl derivative of sphingosine. The sphingosine derivative isthen conjugated with carbamazepine in the presence of triphenylphosphineas described by Kishimoto (Ibid.). The sphingosine-carbamazepineconjugate is then reacted in the presence of pyridine hydrofluoride asdescribed by Matsuura et al. (Ibid.) to remove the t-Boc protectinggroup, to yield the drug/sphingosine conjugate covalently linked throughan amide bond. This reaction scheme is illustrated in FIG. 5.

EXAMPLE 6

The effect of presenting a biologically active compound such as a drugto mammalian cells as a prodrug covalently linked to a polar lipidcarrier moiety was determined as follows. The antifolate drugmethotrexate was conjugated with a variety of polar lipid carriers viaorganic spacer moieties having specific reactive functional groups. Arepresentative sample of such compounds is shown in FIGS. 6A through 6C,wherein MC represents Mtx linked to sphingosine via an amide bond to a6-aminohexanoic acid spacer, ME₆C represents Mtx linked to sphingosinevia an ester linkage to a 6-hydroxyhexanoic acid spacer, and MSCrepresents Mtx linked to sphingosine via a salicylic acid ester linkageto a 6-aminohexanoic acid spacer. Also studied was a conjugate ofazidothymidine linked to sphingosine via an ester linkage to a6-hydroxyhexanoic acid spacer (N-AZT-ceramide; FIG. 6D). The compoundswere tested for their growth inhibitory effects on murine NIH 3T3 cellsgrowing in cell culture. About one million such cells per P100 tissueculture plate were grown in DMEM media supplemented with 10% fetal calfserum (GIBCO, Grand Island, N.Y.) in the presence or absence of agrowth-inhibitory equivalent of each prodrug. Cell numbers weredetermined after 70 hours growth in the presence or absence of theprodrug. In a second set of experiments was included in the growth mediaan amount of a brain homogenate containing an enzymatically-activeesterase.

The results from these experiments are shown in Table I. As can be seenfrom these data, the MC prodrug had no effect on the growth and survivalof the cells. This result did not change upon co-incubation with theesterase-containing brain extract, which was expected due to the natureof the drug/spacer linkage (an amide bond). A different result wasobtained with the ME₆C conjugate. The prodrug was ineffective ininhibiting cell growth or survival in the absence of brain extract. Uponaddition of the brain extract, a significant increase in Mtxcytotoxicity was observed. This is consistent with cleavage of the esterlinkage by the brain extract-derived esterase. A similar result wasobtained with the MCS conjugate, indicating that the brain extractesterase activity was capable of cleaving the salicylic acid ester.

Table II shows the results of drug uptake studies performed with theprodrug -AZT-ceramide. Antiviral amounts of the prodrug conjugate wereadded to NIH 3T3cell cultures, and the antiviral activity of the prodrugwas found to be equivalent to the activity of free AZT. In addition,upon removal of the prodrug, intracellular retention of prodrug wasfound to be up to 15-fold higher than free AZT (Table II) over a 23hperiod.

These results indicate that for Mtx-containing conjugates, the free drugmust be released from the prodrug for biological activity. These resultssuggest that specific release of this drug, and perhaps others, can beachieved using cleavable linker moieties that are specifically cleavedonly in pathogen-infected cells.

TABLE I Sample¹ # cells/plate² Sample³ # cells/plate⁴ Control/FBS 7.8 ×10⁶ Control/FBS   13 × 10⁶ ME₆C/FBS 6.5 × 10⁶ MSC/FBS  2.1 × 10⁶ME₆C/brain 2.7 × 10⁶ MSC/brain 0.51 × 10⁶ Mtx/FBS 0.16 × 10⁶  Mtx/FBS0.13 × 10⁶ Mtx/brain 0.09 × 10⁶  Mtx/brain 0.06 × 10⁶ Control/brain N.D.Control/brain  6.2 × 10⁶ ¹= cells incubated with drug/FBS or drug/brainextract for 1 hour at 37° C. ²= cell growth and survival determined 70hours after drug addition ³= cells incubated with drug/FBS or drug/brainextract for 2 hours at 37° C. ⁴= cell growth and survival determined 72hours after drug addition

TABLE II Time¹ AZT² N-AZT-Ceramide²  0 hr. 6.49 8.45 23 hr. 0.55 7.78 ¹=time between the end of drug treatment and assay for intracellular drugconcentration ²= nM/10⁶ cells

EXAMPLE 7

A neurological agent of the invention is prepared wherein the druglevadopa (LDP) is conjugated to sphingosine via a 6-aminocaproic acidspacer. The primary amino and hydroxyl groups of sphingosine areacylated by reaction with activated N-(levadopa)aminocaproic acidovernight at 40-50° C., followed by base hydrolysis in 0.1N methanolicKOH. The LDP derivative of 6-aminocaproic acid is synthesized byactivating the carboxylic acid moiety of LDP and reacting with6-aminocaproic acid for 2 days at 60-70° C. This reaction is stoppedunder acidic conditions to liberate anhydrides that form under theseconditions.

It should be understood that the foregoing disclosure emphasizes certainspecific embodiments of the invention and that all modifications oralternatives equivalent thereto are within the spirit and scope of theinvention as set forth in the appended claims.

What is claimed is:
 1. A pharmaceutical composition comprising acompound selected from a group consisting of a corticosteroid, asedative, a tranquilizer, a narcotic, an analgesic, an anesthetic, ananticonvulsive or antispasmodic agent, an antiparkinsonian agent, analkaloid, a catecholamine, a muscarine receptor agonist or antagonist, acholinergic receptor agonist or antagonist, a calcium channel blocker, aγ-aminobutyric acid receptor agonist, antagonist, uptake inhibitor, orenhancer, an antidepressant or antimanic agent, an antioxidant or othercompound that mitigates the effects of reactive oxygen species, and anagent for the treatment of ischemia or other vascular disease of thecentral nervous system, and said composition further comprises a polarlipid carrier, two linker functional groups and a spacer, wherein thespacer has a first end and a second end and wherein the polar lipid isattached to the first end of the spacer through a first linkerfunctional group and the compound is attached to the second end of thespacer through a second linker functional group.
 2. A pharmaceuticalcomposition according to claim 1 wherein the spacer allows the compoundto act without being released at an intracellular site and wherein thefirst linker functional group attached to the first end of the spacer isstrong and the second linker functional group attached to the second endof the spacer is weak.
 3. A pharmaceutical composition according toclaim 1 wherein the spacer facilitates the hydrolytic release of thecompound at an intracellular site and wherein the first linkerfunctional group attached to the first end of the spacer is strong andthe second linker functional group attached to the second end of thespacer is weak.
 4. A pharmaceutical composition according to claim 1wherein the spacer facilitates the enzymatic release of the compound atan intracellular site and wherein the first linker functional groupattached to the first end of the spacer is strong and the second linkerfunctional group attached to the second end of the spacer is weak.
 5. Apharmaceutical composition according to claim 1 wherein the polar lipidis acyl camitine, acylated camitine, sphingosine, ceramide, phosphatidylcholine, phosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidylinositol, phosphatidyl serine, cardiolipin or phosphatidic acid.
 6. Apharmaceutical composition comprising a compound selected from a groupconsisting of a corticosteroid, a sedative, a tranquilizer, a narcotic,an analgesic, an anesthetic, an anticonvulsive or antispasmodic agent,an antiparkinsonian agent, an alkaloid, a catecholamine, a muscarinereceptor agonist or antagonist, a cholinergic receptor agonist orantagonist, a calcium channel blocker, a γ-aminobutyric acid receptoragonist, antagonist, uptake inhibitor, or enhancer, an antidepressant orantimanic agent, an antioxidant or other compound that mitigates theeffects of reactive oxygen species, and an agent for the treatment ofischemia or other vascular disease of the central nervous system,wherein each species thereof has a first functional linker group, andsaid composition further comprises a polar lipid carrier having a secondfunctional linker group, wherein the compound is covalently linked tothe polar lipid carrier by a chemical bond between the first and secondfunctional linker groups.
 7. A pharmaceutical composition according toclaim 6 wherein the first functional linker group is a hydroxyl group, aprimary or secondary amino group, a phosphate group or a carboxylic acidgroup.
 8. A pharmaceutical composition according to claim 6 wherein thesecond functional linker group is a hydroxyl group, a primary orsecondary amino group, a phosphate group or a carboxylic acid group. 9.A pharmaceutical composition according to claim 6 wherein the polarlipid is acyl carnitine, acylated camitine, sphingosine, ceramide,phosphatidyl choline, phosphatidyl glycerol, phosphatidyl ethanolamine,phosphatidyl inositol, phosphatidyl serine, cardiolipin or phosphatidicacid.
 10. A pharmaceutical composition according to claim 1 wherein thespacer is a peptide of formula (amino acid)_(n), wherein n is an integerbetween 2 and
 25. 11. A pharmaceutical composition according to claim 10wherein said peptide of formula (amino acid)_(n) comprises n identicalamino acids.
 12. A pharmaceutical composition according to claim 10wherein said peptide of formula (amino acid)_(n) comprises anycombination of n amino acids.